Prefetchable base address capability has to be enabled on the PEX8311 PCI Express to local bus bridge chip to perform 64-bit direct master or DMA transfers. This is of relevance on machines from 4 GB of memory on. The corresponding bits can be set through the configuration EEPROM of the PEX8311. Units with serial number 94 and higher are shipped with this configuration. The EEPROM can be regrogrammed with the PLX Technology SDK.
An Archive with the PROM contents, instructions and software can be found here.